Spatial compounding is a method of creating an ultrasound image by compiling multiple views acquired at different angles. Each view is obtained from multiple lines of sight at different angles. This is a departure from traditional ultrasound imaging that used a single line of sight perpendicular to the scanhead face. The views from the multiple angles are combined to create a single image, thereby reinforcing real-tissue information and suppressing random artifacts. Spatial compounding has resulted in a reduction in speckle noise artifacts; shadowing artifacts and image-degrading artifacts. In addition, such compounding, which is also known as compound imaging, results in improvements in: contrast resolution; needle visualization; tissue contrast resolution; fine-structure delineation; interface/border continuity and lateral edge detection.
The original literature called this technique Compound Imaging. Many companies are now using this technique, calling it various names including: SonoCT; CrossBeam Imaging; and Spatial Compounding.
Some systems use a method where information from both the transmit and the receive beam steering is processed to produce images from multiple view angles. The multiple images are aligned and combined to form an image. Images that are created using both transmit and receive information are typically superior to images consisting of receive information only.
One system for generating sonographic images is to use phased arrays, which, for example, can have 64, 128 (or if desired, any other number) elements. In phased arrays, all of the array elements (64 or 128) must be selectively pulsed to form the wavefront for each scan line. Each scan line has its own unique angle with respect to the transducer face in the sector format. Thus, the geometry of each ray is independent of the geometry from other rays. Electronic focusing is required for both transmitting energy into the subject as well as for receiving the energy reflected back from the target. A phased array typically has a linear geometry, but the shape of the images produced are usually sectors similar to those produced by curved arrays.
As part of the compounding process, image data corresponding to the different views must be resampled, or geometrically aligned to a common set of coordinates, before they are combined. For curved arrays, the symmetry of the beams (i.e, they are equally spaced in angle) simplifies this process because the tables required to perform the resampling are identical for each beam, except for a simple translation. In general, spatial compounding for phased arrays is much more complicated because the beams are typically not equally spaced. Since, as described above, each ray has a unique geometry, the resampling of each ray is also unique to that ray. Thus, because the rays lack symmetry, each beam requires a unique table for registration. Therefore, a very large amount of computation and/or very large tables are required to register the image data from the different views.